The invention relates to sensing blood velocity in tissues such as skin, skin flaps, transplants, breasts, retinas, and internal organs and tissue.
The evaluation of hemodynamics is an important diagnostic subject and has been one of the most difficult challenges in medicine. In skin studies it is important to assess blood velocities over wide areas to determine blood perfusion and predict tissue viability. For surgical procedures involving skin flaps, a reliable method of quantitatively monitoring tissue blood velocity can provide predictive value in assessing tissue conditions during partial detachments and before, during, and after reattachment to avoid tissue necrosis. The same is true in the transplant of tissues and organs and before, during, and following surgery.
The invention is also useful in diagnosing tissue damage due to complications of diabetes, addressing practicality and viability of tissue repairs and vascular densities, and angiogenesis in large sites being studied for possible carcinomas, for example, breast cancer.
It is important to assess blood perfusion and velocities over large areas in real-time and to be able to provide the information to attending medical personnel in manners that are readily perceivable and understandable.
The invention is useful for assessing surgical procedures such as reconstructive surgery involving flaps, the treatment of vascular diseases, the condition of diabetic complications, and the progression of tumors. It can be used to monitor the status of surgically implanted flaps.
Free tissue transfer is a routine surgical procedure with a success rate of up to 95%. Complications generally occur within 48 hours of the initial surgery. Tissue necrosis sets in if poor tissue perfusion is not corrected within 12 hours of surgery. The need for early detection of vascular insufficiency in free flaps is important as the success of corrective surgery strongly depends on the time elapsed since the onset of vascular insufficiency. Between 12 and 17% of flap surgery cases require re-exploration due to post-operative vascular complications that threaten flap viability. Flap salvage rates can be as high as 50%, depending on the procedure and the elapsed time since the onset of vascular occlusion.
Flap viability can be assessed by clinical observations of flap color, tissue turgor, capillary refill, and bleeding after a pinprick, and using monitoring techniques such as laser Doppler velocimetry, differential thermometry, transcutaneous oxygen measurement, plethysmography, and Doppler ultrasound. Clinical visual observation remains the most popular means of assessing tissue viability. Early detection of decreased blood supply to the flap can be detected and corrective action can be taken in time to prevent wide-scale tissue necrosis and possibly eliminate the need for additional surgical procedures.
In the U.S., the breast cancer mortality rate is about 26 per hundred thousand women and the number of deaths due to breast cancer was nearly 44,000 in 1998. Early detection of breast tumors provides a better chance for breast conservation treatment and increases the survival rate. Current methods for detecting breast cancer are based primarily on physical examination and conventional mammography. The invention does not replace mammography as a primary breast tumor screening tool, however, it may serve as an adjunct tool that is economical and portable, and can be used by primary care physicians and gynecologists. It can be used to measure human breasts to estimate subcutaneous blood velocities of normal and diseased breast tissue. The differences between measurements of normal breasts, breasts with benign tumors, and breasts with malignant tumors can be quantified and used to assess the health of the breast.
Measurement of retinal blood velocities is an important application of the invention.
For example, the retina provides direct optical access to both the central nervous system (CNS) and afferent and efferent CNS vasculature. This unique feature has provided generations of ophthalmologists with the ability to evaluate multi-system diseases without invasive diagnostic testing using direct ophthalmoscopy, indirect ophthalmoscopy, and slit lamp biomicroscope examination utilizing 90 or 78 diopter lenses, and the Hruby lens. These methods, however, cannot directly quantify retinal blood velocity, nor do they detect preclinical alterations predictive of eventual significant morbidity. This is particularly pertinent to the insidious onset of glaucoma and macular degeneration. The trend toward preventive medicine prescribes a more sensitive technique to reliably quantify subtle changes in retinal hemodynamics.
Both incoherent and coherent optical techniques have been used to assess microcirculation. The incoherent approach includes the fluorescein dye dilution method and the blue field entoptic method for retinal blood velocity measurement, and plethysmography. The coherent approach is represented by the laser Doppler method and the dynamic laser speckle method. The former employs a focused laser beam to measure the frequency shifts of radiation scattered by a scatterer. It requires a scanning mechanism for imaging applications. Its application to turbid media requires a consideration of multiple scattering effect. The dynamic laser speckle technique has been used for both point measurements and imaging applications in cases where multiple scattering is not prominent, e.g., in monitoring blood and lymph flow in microvessels and in visualizing retinal microcirculation. Taking advantage of the advanced digital photography, the Laser Speckle Contrast Analysis (LSCA) technique extends the conventional laser speckle method to a nonscanning, full-field technique.
Needs exist for improved real-time measurement and display of blood perfusion and velocities. The needs are especially important in skin, skin flaps, surgical sites, transplants, breasts, and retinas, for example.